1. Field of the Invention
The present invention relates to a rotary connector used as electrical connection means for providing a heater device incorporated in a steering apparatus of a motor vehicle or the like and an electronic device such as an air bag system equipped on a car body with an electrical connection.
2. Description of the Related Art
A rotary connector is generally incorporated in a steering apparatus of a motor vehicle or the like and employed as electrical connection means for providing a heater circuit employed in a steering apparatus, an air bag circuit, a horn circuit or other switch circuits, all of which are incorporated in a steering wheel, with an electrical connection. Furthermore, the rotary connector basically comprises a pair of a stationary housing and a movable housing, both being disposed coaxially and connected together so as to be rotatable relatively to each other, an annular space as a cable housing formed between a pair of those stationary and movable housings, a flexible cable housed in the annular space in a manner that the flexible cable can be wound and unwound, and lead blocks correspondingly connected to both ends of the flexible cable.
The flexible cable is constructed so that a plurality of (for example, four pieces of) conductors made of a flat strip of extremely thin copper foil or the like, each conductor being interposed between two sheets of insulating films as a flat strip of base film, are disposed in parallel with each other and stuck to the insulating films.
The rotary connector having such basic construction is further fabricated as follows: fix the stationary housing to the car body while fixing the movable housing to the handle member; and further, connect both ends of the flexible cable to associated electronic devices on the sides of the car body and the handle member via respective lead blocks fixed to the stationary and movable housings; and thereby realizing electrical connection means for providing a heater circuit device for steering apparatus, an air bag system, a horn circuit and/or the like for motor vehicle, with an electrical connection.
That is, the electrical connection means functions when a predetermined current flows through each of a plurality of conductors of the flexible cables.
However, in the above-described rotary connector, the flexible cable is accommodated in a space formed between the stationary housing and the movable housing and is constructed so that a plurality of conductors made of a strip of extremely thin copper (Cu) foil or the like are stuck to the insulating films. As a result, the amount of current allowed to flow through each conductor cannot be made larger than expected.
Additionally, in recent years, it has been seen a phenomenon as a trend that a vehicle primarily used in a cold district is equipped with a steering apparatus constructed such that a heater circuit device to warm a steering (handle) is incorporated therein. The heater circuit device used for the steering is required to supply a relatively large current to a heater device to generate heat therein and therefore, it has been required that the conductor of the flexible cable is able to allow a large current to flow therethrough.
However, when a large current flows through the conductor, such a problem has been seen that the conductor generates excessive heat in some cases and owing to the increase in temperature of the conductor caused by this excessive heat generation, the insulating film is deformed, molten adhesively or the conductor is broken, leading to occurrence of trouble in the function of rotary connector.